src: fix memory leak for v8.serialize

When Buffer::New passes in existing data,
it cannot be garbage collected in js synchronous execution.

Fixes: nodejs#40828
Refs: nodejs#38300

src/node_serdes.cc

@@ -209,9 +209,10 @@ void SerializerContext::ReleaseBuffer(const FunctionCallbackInfo<Value>& args) {
   // Note: Both ValueSerializer and this Buffer::New() variant use malloc()
   // as the underlying allocator.
   std::pair<uint8_t*, size_t> ret = ctx->serializer_.Release();
-  auto buf = Buffer::New(ctx->env(),
+  auto buf = Buffer::Copy(ctx->env(),
                          reinterpret_cast<char*>(ret.first),
                          ret.second);
+  free(ret.first);
 
   if (!buf.IsEmpty()) {
     args.GetReturnValue().Set(buf.ToLocalChecked());

test/parallel/test-v8-serialize-leak.js

@@ -0,0 +1,15 @@
+// Flags: --expose-gc
+const v8 = require('v8');
+const assert = require('assert');
+
+const before = process.memoryUsage.rss();
+
+for (let i = 0; i < 1000000; i++) {
+    v8.serialize("")
+}
+
+gc()
+
+const after = process.memoryUsage.rss();
+
+assert(after - before < 1024 * 1024 * 10, `before=${before} after=${after}`);